1. Field of the Invention
The invention generally relates to improvements in a metal deforming mechanism that drives a tool by a link-actuated tool support. In another aspect, the invention generally relates to improvements in metal deforming by a tool carrier such as a press frame with a guide for a rectilinearly moving tool. More specifically, the invention relates to a bodymaker for producing container bodies from a blank or preformed cup. In a specific application, the invention relates to a bodymaker for forming metal can bodies by a draw-and-iron process. The invention also contemplates the use of a bodymaker for forming cans of materials other than metal, which may include plastic, composites, polymer co-extruded laminate materials, or still other materials.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
The food can, beverage container, and the like have evolved into a sophisticated article of manufacture. The method of forming a container body from metal sheet stock is well known. This process is known as draw-and-iron. The typical steps of this process are described, below. Over many years, variations, improvements and refinements have been applied to the fundamental steps of the method. Some of these steps may have been significantly modified, supplemented, or eliminated according to different practices.
Metal containers are formed from metal sheet stock, which is initially selected to be of a specified thickness that is sufficient to produce a competent end product. For purposes of economy and efficient design of the finished container body, the selected sheet stock is chosen to be as thin as possible. During processing, parts of the sheet stock are greatly reduced in thickness. The ability to adequately manufacture the portions subject to the greatest reduction can be a limiting factor in the determination and selection of the suitable starting sheet stock thickness or the necessary size of the initial blank cut from the sheet stock. Consequently, improved forming techniques can produce significant economies by allowing the use of less metal or other materials than might be required by other techniques. Alternatively, improved forming techniques can improve economy by producing container bodies at a greater rate, with improved quality, and with reduced rejection rate.
The first step for manufacturing a container body of predetermined diameter and height is to form a container blank from metal sheet stock. The metal sheet stock is cut to produce a disc. In a continuous process performed within the same machine that cuts the disc, the disc is preformed into a shallow cup. The cup-shaped blank is considerably wider in diameter and shorter in height then the predetermined diameter and height of the end-product container body.
The wide, cup-shaped blank is fed into a bodymaker, which is a specifically designed punch that employs a linear reciprocating ram to drive the blank through dies in a tool pack. Initially, the bodymaker advances a redraw sleeve against the blank to clamp the blank in aligned position with respect to the path of the ram. In a single stroke, the ram advances along an axial path to engage the blank and to drive the blank along the longitudinal ram axis that extends through the tool pack. The tool pack typically consists of a series of dies supported concentrically about the ram axis. The initial die is a metal deforming redraw die that reconfigures the blank from a shallow, wide cup into a narrower and longer cup of similar diameter to the predetermined diameter of the end-product container body. The subsequent dies of the tool pack are a plurality of ring dies that iron the sidewall of this narrowed blank to form a substantially taller container body. As the ram stroke reaches its maximum extension, the ram drives the bottom of the container body against a bottom-forming doming die that imparts a new shape to the bottom of the can body. The ram then reverses direction. As the ram moves in reverse, compressed air or other means removes the formed can body from the ram and the can body exits the bodymaker.
As produced by the bodymaker, this container body is closed at one end, referred to as the bottom, and open at the other, referred to as the top. In subsequent processing, the open top end is trimmed to define a container body of the predetermined height and to form a uniform edge at the open top end. Typically the trimmed edge is necked-in and flanged, allowing a small lid to be applied. Before the lid is applied, the container body can be filled with selected contents through the open end. The edge of the lid and the edge of the container body are joined together by a seaming process, producing a finished, closed container.
The type of container body with integral sidewall and bottom wall is called a one-piece container body, and the type of finished container formed from this container body and an applied lid is called a two-piece can or two-piece container.
The technology for forming a one-piece container body originated from an effort to produce beverage containers from aluminum metal. The initial technical achievement was to consistently produce a reasonably uniform aluminum container body that could be used for commercial purposes with automated production and filling equipment. This achievement was realized, and the technology subsequently was expanded to produce similar one-piece cans of steel. Cans of similar structure are known in several different materials, now also including plastic.
After the basic techniques for forming one-piece bodies were developed, the technology improved in many respects. One of the dominant goals has been to reduce the cost of each can. Cost reduction typically translates into reducing the amount of raw material, such as aluminum, that is necessary to reliably produce a can body. A reduction in the quantity of metal can be achieved by a variety of modifications. Selecting a thinner starting sheet stock or cutting a disc of smaller diameter will achieve material savings, provided the predetermined end product can be produced reliably. According to other schemes, the initial blank can be cut in a special configuration that employs a reduced quantity of metal.
Each part of the can has been designed and refined to minimize wall thickness to the extent possible with each progressive advance in technology. Thus, the raw sheet stock needed to produce a one-piece container body is now considerably thinner than was necessary several decades ago. The thickness of present day aluminum sheet stock is in the range from 0.010 to 0.011 inches. The sidewall profile of a one-piece aluminum container body reflects the sophistication of various technological advances, with the specification for sidewall thickness at the center of the can height being about 0.004 inches or 0.1 mm, which is extremely thin. The sidewall lends itself to the greatest amount of working in the bodymaker and, thus, tends to be the thinnest portion of the container body. The bottom end is considerably thicker but is far more difficult to work into a thinner structure. Thus, the sidewall is considered to be the limiting structure of the container body. The minimum thickness of the starting sheet stock or the minimum diameter of the blank disc is limited by the ability of the forming equipment to form the sidewall.
To mass-produce container bodies of such thinness requires reliable precision in the equipment that manufactures the container body. If the reliable level of precision can be increased, then various benefits and cost savings become possible. On one hand, the rejection rate or scrap rate might be reduced, reflecting that a larger percent of the container bodies coming from a bodymaker are of useable quality. On the other hand, it may be possible to achieve additional reductions in specified wall thickness, where a present specification of wall thickness incorporates provision for lack-of-precision in the manufacturing process. For example, the specification of sidewall thickness may accommodate known or expected inaccuracy in bodymaker performance. Opposite side areas of a can body sidewall may be, respectively, a thin side and the thick side, perhaps averaging about 0.004 in. The deviations or tolerances between the top or bottom locations of the thin wall are about 0.0005 inches in a standard bodymaker of prior art construction.
It would be desirable to minimize or almost totally eliminate this deviation. Eliminating this deviation should result in substantial savings of can wall material. Better accuracy in the bodymaker enables a further possible cost reduction from an improved ability to use a different alloy or material content. Still another saving may arise by the ability to operate the bodymaker at a higher speed. The exact source and amount of cost savings is subject to future development, but expectation that better accuracy in bodymaker performance will lead to savings is well accepted.
It was recognized in the early days of forming one-piece container bodies that the original rotary motion of a motor must be translated into near-linear motion in order to drive a container body blank along a linear axis through forming dies of a tool pack. Initial bodymakers employed the slider-crank mechanism, which remains the mechanism in active use, today. A slider-crank mechanism converts circular motion into oscillating linear motion.
Rotary or circular motion is the essential driving output of commercial motors and is the power source for the vast majority of industrial machines. Rotary motors are a preferred drive mechanism for many applications where reciprocating motion is required in a cycle of machine operation. A rotary motor can drive a rotary operating mechanism such as a crank arm, which rotates in a first or forward direction for one half of its cycle and then completes its rotary cycle in an opposite or rearward direction for the second half of each cycle. Rotary motion is highly desirable because it enables a machine to reciprocate without altering the rotational direction of motor operation. The motor can continue to operate at high speed, in a single direction of rotation. In addition, a flywheel is desirable in a bodymaker because it adds rotating mass. Often a rotary electric motor will drive a flywheel that carries the crank arm or operates on a concentric axis with the crank arm.
Interest in converting rotary motion into near-linear motion rose to considerable importance in the eighteenth century when American inventor James Watt and others developed industrial machinery including steam engines and railroad engines. A large number of conversion linkages were developed, although none are considered to be exact. In the nineteenth century, the French engineer, Peaucellier, and Russian mathematician, Lipkin, independently developed an eight-bar linkage that is regarded as the first to produce exact straight-line motion. This linkage, now known as the Peaucellier Straight-line Mechanism, is a diamond shaped linkage of four pivoted bars with two opposite pivot points cross-connected by a two-part bar that is pivoted at its center. This linkage has been applied to can bodymakers but has the disadvantage of employing pivoting links that must, to some degree, rock or reciprocate. It is generally desirable in a bodymaker to minimize the number of rocking or reciprocating parts and the overall mass of reciprocating elements.
While the Peaucellier mechanism produces a straight line, it complicates the component linkages between a drive system and a ram. The added linkages augment the moving mass of slider-crank motion, increasing the mass that periodically must be reversed. It would be desirable to employ a technology that substantially eliminates the inherent inaccuracy associated with a slider-crank motion. For this purpose, it would be desirable to employ a movement based on rolling motion or rotation of substantially all elements. A hypocycloid straight-line mechanism employs the mathematical relationship between one circle rolling inside another circle to define a straight line. A point on the circumference of a circle rolling on the inside of another circle generates a curve called a hypocycloid. When the diameter of the rolling circle is one half that of the outer circle, the curve traced by a point on the circumference of the smaller circle is a true straight line. This concept is demonstrated by use of a planetary gear that can be rotated around the inside circumference of a ring gear to move a slider with straight motion.
Certain linear motors and mechanisms for converting linear motion to rotary motion are known, but their application to a bodymaker is limited by many factors. A first is that hypocycloid motor seeks to convert linear motion of a piston to rotary motion of a driven wheel, which is the opposite force pattern required in a bodymaker. A second is that a bodymaker tends to employ considerable moving mass. A bodymaker is expected to drive the ram with a force from about eight thousand to twelve thousand pounds in order to produce a metal can body. This force must be produced on each stroke of the ram at a rate of several hundred strokes per minute. The stroke of the ram must reverse with the same frequency in order to withdraw the ram after each forward stroke. Withdrawing the ram is necessary in order to discharge the formed container body and to receive a new can body blank for use in the next stroke. Many linear drive devices are poorly suited to drive a substantial mass through acceleration, deceleration, and direction reversal, while achieving the necessary force levels per stroke and while achieving smooth and nearly vibration-free operation. Thus, force, speed, and prompt reversal must be achieved in a compact space suited for use in a factory, in an industrial can line, which is a series of machines that work in sequence within a manufacturing plant to produce a finished can body. In meeting these combined requirements, the rotary motor is the clear choice of driver, and a driven, rotating large mass such as a flywheel with a crank arm and slider are a capable solution.
U.S. Pat. No. 3,696,657 to John Hardy Maytag is often regarded as being the pioneering patent in the art of bodymakers. The general arrangement of Maytag's bodymaker remains in use, although with modifications. Maytag employs a classic slider-crank mechanism in which a rotary motor drives a crank arm, which likewise operates in a rotary cycle. The crank arm often is considered to rotate on a Z-axis of an X-Y-Z axis coordinate system. A first or rear end of a main connecting rod is rotatably connected to the crank arm at a predetermined throw length or working radius from the center of crank rotation. The front or second end of the main connecting rod was connected via intermediate linkages to the bodymaker ram. In turn, the ram was mounted on a carriage and guided by rollers traveling over linear carriageway strips to accurately guide the ram for movement along a linear axis aligned with the tool pack.
The reciprocal, forward and rearward motion of the ram can be regarded as X-axis movement. Likewise, the crank throws of the crank arm produce an X-axis component at the forward and rearward ends of each half-cycle that brings the ram to its respective forward and rearward extreme positions. However, the rotary action of the crank inherently adds an additional Y-axis or lateral offset component at all rotary positions intermediate to the end points of the forward and rearward half-cycles. Thus, the main connecting rod moves with rocking motion wherein the first end of the connecting rod follows a circular path that not only provides a useful reciprocal component with respect to an X-axis but also provides an undesirable deviation along a Y-axis. The Y-axis components are considered to contribute vibration to the bodymaker as a whole and to cause inaccuracy or limited accuracy in the linear, X-axis motion of the ram. Misalignments of the ram as small as about 0.0005 to 0.0010 inch can produce defective can bodies in a bodymaker. Vibration in the bodymaker as a whole contributes to wear on all moving parts and resultant loss of precision.
The Maytag patent teaches the adaptation of a straight-line motion assembly acting between the connecting rod and the ram to offset vibration or misalignment. This assembly employs a cross-head with side thrust resisting levers. In addition, the carriageway and rollers are intended to ensure the linear accuracy of ram motion. This basic arrangement and subsequent refinements of it have proven successful in producing one-piece can bodies for many years. However, the cross-head and carriageway are less than perfect in eliminating vibration or deviations from linearity. To at least some degree, the Y-axis deviations introduced in the vertical plane by a rotary crank can add vibration or misalignment to a ram. At certain levels of accuracy, the deviation may be of little importance. For example, at a specified container sidewall thickness of 0.004 inch, the inaccuracy caused by deviations may be absorbed in the acceptable tolerance from the specified sidewall thickness. However, a level of technology will be reached at which the deviations become the limiting factor that prevents further savings of costs and materials.
Efforts to improve the accuracy of the Maytag bodymaker largely have focused upon better support and centering for the ram, while continuing to employ the slider-crank mechanism. U.S. Pat. No. 4,934,167 to Grims et al. shows modifications of the Maytag bodymaker, wherein liquid or hydrostatic bearings support the ram carriage. In addition, liquid bearings carry the ram carriage on a pair of guide rods to further ensure accurate linear movement with low friction. U.S. Pat. No. 5,257,523 to Hahn et al. shows modification of the Maytag and Grims patents, using electromagnets responsive to ram position to maintain the ram in radially centered position. U.S. Pat. No. 5,335,532 to Mueller et al. shows a counterbalance structure that is reciprocated opposite to movement of the ram, with a perpendicular component, to compensate for X-axis, Y-axis and Z-axis vibration. U.S. Pat. No. 5,546,785 to Platt et al. shows a split crank that allows adjustment of the crank throw so that different crank throws can be selected to alter the ram's travel. This adjustability permits a single bodymaker to produce can bodies of different sizes. U.S. Pat. No. 5,564,300 to Mueller shows the replacement of Maytag's cross-head with a version of the Peaucellier Straight-line Mechanism that supports linear motion of the ram.
Another bodymaker design is taught in U.S. Pat. No. 4,173,138 to Main et al, which continues to employ the slider-crank mechanism. In this design, also, a rotary motor conventionally drives a crank arm on the Z-axis. Various connecting rods and arms are linked together between the crank arm and ram, but the linkage concludes with a drive rod having both a front end that is intended to move on the X-axis and a rear end that moves over an arc having both X-axis and Y-axis components, nonlinearly. The front end of the drive rod imparts X-axis driving motion to the ram. In turn, the ram is supported on two spaced-apart, stationary bearings for guiding the ram on a linear axis with precision. The various bearings on the drive rod and the ram are hydrostatic oil bearings, which have good precision aligning or self-centering properties.
The inherent problems of slider-crank mechanisms are acknowledged in U.S. Pat. No. 4,956,990 to Williams, which shows a ram reciprocated by a wobble mechanism. The disclosed ram drive mechanism reciprocates the ram on the X-axis by applying reciprocal forces to a transverse rod that is connected at its center to the ram. Opposite ends of the transverse rod each engage a different wheel of a powered, synchronized pair of counter-rotating wheels that turn on a common axis lying perpendicular to the ram in the Y-Z plane and that are positioned on opposite edges of the ram. Each end of the transverse rod engages one of the wheels at a working radius.
The operational path of the transverse rod is complex and might best be described as requiring wobble. The wheels are synchronized to bring both rod ends simultaneously to a forward position, advancing the ram, and simultaneously to a rearward position, withdrawing the ram. However, at all positions along the X-axis intermediate the forward and rearward extremes, the counter-rotating wheels cause the transverse rod to tilt or wobble in the Y-Z plane. Thus, at such intermediate positions, the rod either slightly rotates the ram or requires that its center connection to the ram have rotational pivoting ability. Also, the effective length of the rod changes between a minimum length at the forward and rearward extreme positions and a greater but varying length requirement throughout the intermediate wobbling positions. Due to these many complexities of motion, high-speed, stable operation would be difficult to achieve.
Still another design for a bodymaker with reduced lateral deflections of the ram appears in U.S. Pat. No. 5,735,165 to Schockman et al. Two side-by-side, counter rotating cranks operate in parallel to actuate a Scotch yoke assembly that linearly drives a pair of rams. The Scotch yoke is an open frame that is reciprocated along an X-axis on a pair of guideposts. In turn, the open frame linearly reciprocates the rams in unison. The cranks reciprocate the frame by providing rotary motion on a pair of Z-axes. With respect to the X-dimension only, the throws of the two cranks are engaged in slider blocks that fit snugly within the open center of the frame, such that the rotating cranks reciprocate the frame on the X-axis.
The open center of the Scotch yoke frame is elongated in the Y-dimension. Each crank throw is mounted in a slider block that is slidable in the open frame along the Y-axis. Consequently, rotation of the crank causes each crank throw in a slider block to slide freely within the center of the frame on the Y-axis, thereby expending motion along the Y-axis without introducing deflections having a Y-component to the frame. As a result, the cranks move the frame with what is intended to be only X-axis movement.
This arrangement has the disadvantage of operating at least two parallel mechanisms in synchronization. Unevenness between the two mechanisms can skew the Scotch yoke and produce binding or excessive wear. The sliding between each of the slider blocks and the frame of the Scotch yoke is substantial, covering a distance equal to the length of the ram throw. During high-speed operation, such substantial lateral sliding motion can introduce a high rate of wear, generate heat, change clearances, and introduce distortion. The free motion of the crank throws along the Y-axis produces constantly shifting drive points for powering X-axis movement, which creates a complex system of forces in which control of vibration can be difficult. These disadvantages can limit operating speed and require high maintenance of a Scotch yoke drive system in a bodymaker.
The production ability of commercial bodymakers has been limited for many years. Some manufacturers of successful bodymakers suggest that their bodymakers can achieve 400 cans per minute, more or less. In practice, sustained production speeds tend to be below this figure, perhaps closer to 350 cans per minute. These figures are believed to fairly represent the state of the art, according to the generally accepted ability of the bodymaker designs and improvements of the above patents that have achieved commercial success.
It would be desirable to produce straight-line motion in the ram of a bodymaker from a continuous rotary drive system by using a planetary gear mechanism capable of converting rotary motion of a motor or wheel to linear motion of the ram without the presence of a vertical thrust component. It would be particularly desirable to employ continuous rotary motion throughout a drive system to the driving connection with the ram, which would obviate the use of a rocking link or wobbling link between the drive system and ram. Continuous rotary systems offer optimal opportunity to achieve high-speed operation.
Further, the bearings and other low friction mechanisms for rotary systems are highly advanced, operate with precision, and have long life. Therefore, continuous rotary systems are the clear choice for high-speed, durable, and accurate machinery. It would be desirable to employ continuous rotary devices throughout the drive system of a bodymaker, converting to reciprocating linear motion only at the latest possible point in the drive system. For example, the bodymaker ram itself reciprocates on a linear, X-axis, for best operation. Ideally, the ram should be substantially the only component of the bodymaker that reciprocates, requires support of linear bearings, or requires that a substantial mass undergo periodic diametric reversal of direction.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the method and apparatus of this invention may comprise the following.